Waterproofing multifamily balconies: Common mistakes leading to major failures

by sadia_badhon | January 4, 2019 9:33 am

by John Igo

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Private balconies have long been a sought-after amenity in multifamily dwellings for renters of all demographics. However, apartment developers, builders, and designers often dislike balconies due to the added expense, complexity, and risk of failure from water. With careful attention to details, it is possible to design and build functional, aesthetically pleasing, and leakproof balconies.

Balconies involve many different trades, such as framers, painters, electricians, occasionally a plumber, ironworkers, concrete contractors, and waterproofers. Individuals involved with each of these trades do not necessarily understand what the other trades need to be successful on the construction of this important element.

Balconies increase the cost of every unit constructed. Every balcony on a project brings with it a host of issues, such as additional framing and doors, railings, sequencing problems, and jobsite safety considerations. Most importantly, these elements bring liability due to the risk of failure that is shared by almost every entity involved in the project from conception to delivery. Unfortunately, it is also shared by future tenants.

Six dead and seven injured in Berkeley

Six college students died when a balcony on the fourth floor of an apartment building collapsed in Berkeley, California, in June 2015. As a result of poor construction, wooden support beams that rotted due to water intrusion gave way at the worst possible moment, turning a celebration among friends into a tragedy. This singular event proves that when given the opportunity, water and time always win the battle. One only has to stand at the rim of the Grand Canyon to realize the absolute truth of this statement. It is the responsibility of professionals in the construction industry to both clients and future tenants to design and install systems in a way ensuring water does not have a fighting chance, yet still offer the amenity of a balcony to enhance apartment dwellers’ quality of life.

This author has spent the past eight years wrestling with the challenges of balcony waterproofing in multifamily construction as waterproofer, building materials supplier, and product developer. Throughout all of the research and conversations, it has become clear there is no consensus on the ‘right way’ to design and build a proper balcony. However, this author has, over the years, encountered many of the same mistakes pertaining to balcony design and installation. This has led to the conclusion balconies do not inherently require risk. Sound, proven practices can be employed to deliver leakproof balconies with the ability to stand the test of time.

Design mistakes

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This article addresses many of the common misconceptions and mistakes this author has encountered over the years and provides consensus-building ideas for a very important amenity in the multifamily construction world.

Sloping trusses

One of the only reliable constants in construction is gravity. This force is known, quantified, and calculated into almost every aspect of engineering and design. For this reason, it is surprising wood-framed balconies are designed without slope built into the trusses or joists supporting the decks. Slope in the deck substrate should be the first line of defense to move water away from the building. Gravity is a friend to an architect in very few places, and balcony waterproofing is one of them.

A percentage of the deck in flat-framed balconies is always slightly pitched back to the building. The most effective way to defeat water is to limit the time it has to interact with the building. Sloping the substrate ensures water flows out of the weep system at the balcony face and spends as little time in interaction with the waterproofing system as possible. If the thinking is sloped concrete removes water from a balcony, it is important to note while water on the surface of the concrete is free, one will eventually pay dearly for any water trapped beneath the concrete. Providing proper slope in the framing reduces the risk of improper drainage.

Incorrect drain mats

The use of drain mats, or drainage composites, beneath concrete wear surfaces is growing in popularity, and in general it is a good idea. Unfortunately, most drain mats specified are engineered for below-grade drainage and designed to be high in compression resistance and provide a high flow rate when under heavy loads. Typically between 6.5 and 13 mm (¼ and ½ in.), these drain mats are too thick and this reduces the thickness of the concrete at the face of the balcony.

Balcony drain mats do not need to withstand high dead loads and are not required to provide a high flow rate. One does not need to filter 76 L (20 gal) per minute from beneath the concrete, but a path must be provided for water to exit once it arrives there. Specifiers should select appropriate low-profile drain mats (3.2 mm [¹/8 in.] is suitable) that are a solid sheet of studded membrane bonded with a filter fabric to allow for moisture transmission. This low profile is the key to durability of the concrete along the perimeter of the balcony where the concrete meets the pour stop (usually an aluminum ‘T-bar’ integrating a drip edge along the perimeter).

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Further, drain mats should only be used in settings where slope is designed into the deck. Employing mats in a corridor without a slope only creates a subsurface ‘lake’ in which water can reside. This subsurface water causes efflorescence in the concrete and eventually results in premature failure of the waterproofing system.

Improperly placing railing mounts

The best way to protect a waterproofing system is to mount the railings on the face of the balcony below the T-bar. Many designers do not like the appearance of this method, and it still poses its own unique problems with water infiltration at the mounting holes. Surface mounting railings, especially the supporting members along the length of the railing, can be done safely and cost effectively. However, a few principles should be kept in mind when designing the balcony, including:

• stanchions embedded in the concrete should be placed at least 76 mm (3 in.) from the edge of the balcony;
• stanchions should be no closer than 203 mm (8 in.)from any wall or column; and
• every embedded railing stanchion is an opportunity for a leak, and therefore should be used as sparingly as possible.

Ignoring these guidelines creates difficulties during waterproofing as it becomes impractical (if not impossible) to properly lap and seal all the components (Figure 1). Apart from adding unnecessary cost, there are simply too many elements to fit into a small space while still guaranteeing proper installation and performance of the waterproofing system.

Incorrectly designed scuppers

While scuppers effectively drain water from the surface of the concrete, they should also capture and evacuate the water draining from beneath the concrete. The waterproofing system should terminate into the opening of the scuppers so water flowing down the surface of the waterproofing (below the wear surface if they are unique) has a path to escape.

Cricketing balconies with parapet walls

Balconies enclosed by a wall are a special amenity and enhance the visual appearance of a façade. Even with proper sloping of the deck, the water beneath the concrete will flow into an intersection with the wall before reaching the scuppers. Proper cricketing of the balcony deck and an adequate number of scuppers are crucial in this type of design.

Using lightweight concrete

Many specifications refer to balcony concrete as ‘lightweight.’ Normal pea gravel ‘hard rock’ concrete at 20,000 kPa (3000 psi) is adequate for most private balconies and breezeways. At a 50-mm (2-in.) thickness, this only adds 11 to 13.5 kg (25 to 30 lb) of dead load per square foot to the structure. Lightweight concretes rely on aggregate too large for most small concrete pumps used in the market, thereby driving up the cost of the concrete exponentially due to the expense of materials and pump rentals. Using lightweight concrete also increases the difficulty of achieving a good broom finish, resulting in a less attractive finished product.

Replacing galvanized metal flashing

In recent years, some manufacturers have introduced a 2.6-mm (105-mil) membrane that, in theory, can be used to eliminate the need for galvanized L-flashing to transition from vertical to horizontal surfaces. In practice, this transition is often complicated by the fact framing is not finish carpentry. There will always be gaps of 13 mm (½ in.), or more, at this critical change of plane, leaving a 2.6-mm membrane to bridge the gap for the life of the balcony (Figure 2).

Galvanized wall flashing provides a clean, strong substrate to bridge these framing gaps and eliminates the risk of membrane failure due to the presence of a large void.  Finally, many are under the impression galvanized flashing is a waterproofing layer. It is not. It is merely a substrate to make the transition at changes of plane. When water reaches galvanized wall flashing behind the membrane, the war is already lost.

Creating natural wood columns

As waterproofing wraps natural wood columns when they are completed, they must be covered with a decorative finish at the base. The big challenge here is wood columns will almost certainly split and crack as they age, allowing water to permeate behind the waterproofing wrapped around their bases. Therefore, columns should always be clad with finishes to withstand weathering and limit penetration of the structural column of the elements.

Incorrect product specification

Multifamily projects often use a variety of products from multiple manufacturers to complete a waterproofing system. This creates its own set of difficulties as care must be taken to ensure every component is compatible with other specified products. If and when failures occur, the finger-pointing game will ensue among the various manufacturers. Reaching a final determination for the cause of the problem will be difficult as each party seeks to limit its exposure. This can be addressed by finding a manufacturer that can offer a complete turn-key system backed by a warranty, not just product warranties for the individual components used.

Sequencing mistakes

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A perfect design on paper still needs to be implemented correctly in the field to ensure the system performs properly. Through experience, this author has found the following are the most common causes of failures. Thankfully, all of them can be corrected with consistent field training and attention to detail.

Pre-flashing doors

Multifamily builders and subcontractors have long employed the practice of installing a partial waterproofing system in patio doors and along walls for a few very good reasons. It allows them to set the doors more quickly and allows the siding and cornice work to commence in a timely manner. However, this practice is the single most detrimental waterproofing element on the market and must stop.

The foundation of any good waterproofing system is eliminating reverse laps in the membrane. One must make gravity do the work or it will work against the project goals. ‘Pre-flashing’ prohibits the membrane on the deck from being turned up the walls so it properly creates a double barrier along the balcony perimeter. If the deck membrane wraps up the walls and the wall membrane laps down properly over it, even a wrinkle in the wall membrane will not result in a failure because the water simply cannot climb the wall behind it (Figure 3).

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The absolute best practice is to develop a turnkey strategy to balcony waterproofing and concrete placement. Balconies should be fully waterproofed, flood tested overnight, and receive concrete the next day. This is a winning formula this author has followed for several years, and it has paid immeasurable dividends. Failure rates have plummeted to almost zero in this author’s experience.

Excessive use of sealant

Most of the time, thick gobs of sealant are hiding a problem. Used properly, mastics and sealants add a ‘belt and suspenders’ to good waterproofing. When contractors bury an area with a thick bed of these materials, they are indicating they are uncomfortable with how the area was designed, specified, or framed, so they decided to cover it with sealant for good measure (Figure 4).

The problem is adding more mastics and sealants will not address poor design or installation skill. Many such materials employed in waterproofing rely on the evaporation of a solvent to fully cure. Thick beds of sealant will skin over and trap the solvent, creating an airtight pocket as if it were still in the original package. This prevents a full cure of the material and allows displacement when pressure is placed on it by the installation of the wear surface. Sealants applied in a thin layer cure fully, will not hide any issues, and perform as intended.

Allowing extended exposure of the membrane

Most product manufacturers limit the amount of time the membrane can be exposed to ultraviolet (UV) light, with some products having an exposure recommendation as short as 14 days. It is important to be aware of these limitations and ensure precautions are taken to reduce the exposure to match this window. UV is not the only hazard one must guard against. Balconies on any jobsite receive traffic and often become a staging area for construction waste. This exposes the membrane to repeated foot traffic, nail-embedded lumber scraps, and sheet metal and pipes. This is also another reason for not pre-flashing balconies, as the practice jeopardizes the integrity of even the best products on the market (Figure 5).

Honoring proprietary methods

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Frequently, value engineering happens on a project to meet budgetary demands. In waterproofing, some materials and methods are proprietary and substitutions for equivalents can be a challenge. Copycat products must be designed to work around the intellectual property of the original specification, thus running the risk of not offering the same level of performance. They also have the potential of opening up the project in question to patent-infringement litigation. While it is easy to target the waterproofing system to reduce costs, it is pertinent to note the high cost of cutting corners on an element is worth less than half a percent of the total cost of the project.

Flood testing every balcony

Even the best installers have bad days. Flood testing is not optional or difficult. It is the cheapest insurance one can buy. The cost of added time and effort to flood test 100 percent of the balconies on every job is offset by the claims that are prevented by this testing.

The November 2013 article, “Ensuring Balcony Durability: Waterproofing details that stand the test of time[7],” in The Construction Specifier cited a study in which 40 percent of 200 balconies inspected had undetected water damage. Flood testing is the only way to ensure the system is working as intended.

Maintenance mistakes

Well-built systems are still subject to damage over time from the elements and ill-informed maintenance efforts. Educating property maintenance teams on how to properly care for wear surfaces and be mindful of possible exposure points to waterproofing systems will help to ensure a long service life.

Frequent power washing

A common practice in property management is to use power washing to clean stains off of the concrete in corridors. Power washing allows water to ignore the effects of gravity as external pressure pushes it into any available opening. If power washing is necessary, the number of times it is done should be limited and design/construction professionals should be aware water will infiltrate the building envelope if the corridor is not fully waterproofed. Excessive power washing can also damage waterproofing when the water jet hits the membrane beneath the base trim or through cracks existing in expansion joints. Instead 
of frequent power washing, it is advisable to apply a sealer to the concrete so stains cannot penetrate.

Maintaining caulk and sealants

Door trims, joints in siding, electrical outlets, and light fixtures are sealed with caulk to keep water from getting behind the cladding. They should be inspected and maintained regularly. Often, a sealant failure at one of these points is mistaken for a balcony leak.

Conclusion

The design, installation, and maintenance mistakes identified in this article do not need to remain common. The frequency of leaks and failures experienced today are needless. It is possible to design and build functional, aesthetically pleasing, and leakproof balconies. The key is to pay attention to the details at every step of the process and not allow anyone to improvise a detail not shown in the drawings. Framing, railings, sealants, waterproofing materials, building wrap, doors, and drains work together to create a successful balcony project.

If the entire team, including architects and subcontractors, is not instructed on the proper means and methods, one will risk continued failures. General contractors (GCs) and subcontractors can be very inventive, and this well-intentioned problem solving can result in a repeated error in the waterproofing throughout a project. Good drawings and sequencing instructions alleviate the responsibility of design from GCs and subcontractors and drastically reduce the risk of systematic errors. The battle against water can be won, but it requires close attention to the details in the design process and a hypervigilant quality control (QC) program in the field.

John Igo is president of Formulated Materials, a company that both develops and markets multifamily waterproofing and floor underlayment systems and construction equipment through its corporate affiliates and a network of licensed and trained installers. Igo has been a product developer for the multifamily construction industry since 2004 and has developed a passion for leakproof balconies and floors that do not fail. He can be reached at info@formulatedmaterials.com[8].

Source URL: https://www.constructionspecifier.com/waterproofing-multifamily-balconies-common-mistakes-leading-to-major-failures/

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